Blender 2.8 causes all other versions to not run!
Running older versions of Blender alongside 2.8

Blender 2.8 removes older Blender version installed in C:\Program Files\Blender Foundation. If you want to run old versions of Blender alongside Blender 2.8 you will need to download their archive version which doesn't require installation. 


Download the desired version as .zip, 
Extract it
Open the extracted folder
Create a shortcut to the blender.exe 

4.1 Right click on blender.exe and select Create Shortcut 

4.2 Rename the shortcut to differentiate it from the other Blender versions

4.3 Drag the shortcut to your desktop


How to troubleshoot your Blender 2.8 installation on Windows

The first step is always to check if your system fulfills the minimum requirements to run Blender 2.8 and update your graphics drivers. Since you've already done both, you can continue with the following checks.

When Blender's UI doesn't start and it's frozen at the console, make sure that you haven't accidentally enabled QuickEdit mode by clicking into the command prompt. Simply press enter in the console and see if the execution resumes.

Blender offers batch scripts for debugging on Windows which can be found in the folder where Blender is installed. On Linux and macOS these have to be enabled by starting Blender from the terminal with one of the corresponding debug flags. 

blender_factory_startup.cmd allows you start Blender with factory settings, in case your configuration or startup.blend is broken. The batch script uses the --factory-startup flag.

If that command allows you to open Blender properly, make the changes permanent.


File > Defaults > Save Startup File
Edit > Preferences

2.1 Click the icon in the bottom left corner

2.2 Click Save Preferences


If you're experiencing a crash that doesn't happen when starting Blender and you've got an updated graphics driver, then it's likely a bug. In order to help us identify if it's truly a bug and whether this is an issue already reported to the developers, you can run blender_debug_log.cmd. This batch script uses the --debug flag. Once Blender has started, try to perform the same steps that led to a crash. Once you were able to recreate the crash while running Blender from this batch script, upload the created log files (e.g. to Google Drive) and add a link to it in your question so we can take a look at it. Be aware that the blender_system_info.txt file contains detailed system information in case you don't want to share this information publicly.

Depending on the outcome we may advise you to create a bug report on https://developer.blender.org/ where the developers of Blender will try to resolve your problem. If we advise you to create a bug report and you're able to open Blender, go to Help > Report a Bug. In case you can't open Blender use the template and attach your system information file created in the previous step. Make sure to describe your problem in a concise but precise way. Add step by step instructions that allowed you to crash Blender. This is important so that the developers are able to reproduce the conditions that led to the crash. Finally if the crash only occurs with a certain project, you can attach your .blend file. Try to remove everything unnecessary out of the project, so that you have a minimum working example with which you can still reproduce the crash.

The other batch scripts or command line flags should only be used if a developer requests you to run these, because the log files can get quite big.